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Informative site

Informative site is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Informative site rather than just read about it. In short: In phylogenetics, informative site is a term used when maximum parsimony is the optimality criterion for construction of a phylogenetic tree. It refers to a characteristic for which the number of character-state evolutionary changes of at this site depends on the topology of the tree.

Informative site — main illustration
Informative site — illustration

Key takeaways

  • Informative site belongs to biology; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Informative site to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Informative site from memory before moving on to harder problems.

Reference excerpt

In phylogenetics, informative site is a term used when maximum parsimony is the optimality criterion for construction of a phylogenetic tree. It refers to a characteristic for which the number of character-state evolutionary changes of at this site depends on the topology of the tree. The characteristics can take on multiple types of data, including morphological (such as the presence of wings, tentacles, etc.) or molecular information such as sequences of DNA or proteins. The informative site is a position in the relevant set of aligned sequences at which there are at least two different character states and each of those states occurs in at least two of the sequences. In other words, it cannot be a fully conserved (i.e., invariable) site nor can it be a (singleton) site with a difference in only one sequence (as seen, for example, in single-nucleotide polymorphisms and single-nucleotide variants). In both cases, the number of character-state changes is the same regardless of the topology of the tree, equal to 0 and 1 respectively.

References

Illustrations

Informative site: Example of parsimony informative sites. The sites 2 and 4 are informative, while sites 1 and 3 represent the two types of uninformative sites (invariable and singleton respectively). Site 2 indicates a grouping of Species A and C, while site 4 indicates a grouping of Species A and B. Because these two sites conflict, other analyses (such as maximum likelihood) are needed to resolve the phylogenetic tree of these four species.
Example of parsimony informative sites. The sites 2 and 4 are informative, while sites 1 and 3 represent the two types of uninformative sites (invariable and singleton respectively). Site 2 indicates a grouping of Species A and C, while site 4 indicates a grouping of Species A and B. Because these two sites conflict, other analyses (such as maximum likelihood) are needed to resolve the phylogenetic tree of these four species.

Worked examples

Example 1 — a first encounter with Informative site

Start with the simplest possible case. Write down what Informative site claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Informative site before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Informative site ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Informative site

In research
Informative site appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Informative site in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Informative site is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bioinformatics stubs, Computational phylogenetics, so understanding it makes those chapters shorter.
In everyday life
Look for Informative site outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Informative site in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Informative site means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Informative site out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Informative site in simple terms?

In phylogenetics, informative site is a term used when maximum parsimony is the optimality criterion for construction of a phylogenetic tree. It refers to a characteristic for which the number of character-state evolutionary changes of at this site depends on the topology of the tree.

Why does Informative site matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Informative site?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Informative site.

Tags

  • Bioinformatics stubs
  • Computational phylogenetics

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